The storage of data in scrambled form is currently developing rapidly. For example, the audio video digital data transmitted in compressed and scrambled form are generally recorded in this form so as to control access to these data. They are therefore descrambled only when the corresponding images are viewed. Another example relates to the 1394 digital bus, solutions envisaged within the framework of the exploitation of this digital bus being the transmission of digital data in scrambled form and hence their storage in this form.
A problem connected with this recording of digital video data streams in scrambled form relates to the exploitation of particular modes of reading or special modes referred to hereinafter as the “trick mode”, using the terminology of the MPEG standard, this term encompassing among other things the following functions: fast forward, fast rewind, slow motion, accelerated motion, freeze frame. These functions actually require access and fast decoding of these recorded data, conditions which are difficult to make compatible with recording in scrambled mode.